This disclosure relates to a medical device and more particularly to an implantable therapeutic substance delivery device with a piston operated pump.
The medical device industry produces a wide variety of electronic and mechanical devices for treating patient medical conditions such as pacemakers, defribulators, neurostimulators, and therapeutic substance delivery pumps. Medical devices can be configured to be surgically implanted or connected externally to the patient receiving treatment. Clinicians use medical devices alone or in combination with therapeutic substance therapies and surgery to treat patient medical conditions. For some medical conditions, medical devices provide the best, and sometimes the only, therapy to restore an individual to a more healthful condition and a fuller life. Implantable drug delivery pumps can be used to treat conditions such as pain, spasticity, cancer, and a wide variety of other medical conditions.
An implantable drug delivery pump is implanted by a clinician into a patient at a location appropriate for the therapy that interferes as little as practicable with patient activity such as subcutaneous in the lower abdomen. Typically, a drug delivery catheter is connected to the drug pump outlet and implanted to infuse the drug, infusate or other therapeutic substance at a programmed infusion rate and predetermined location to treat the medical condition. Reliable and accurate operation of the drug pump is important because both inadequate and unintended therapeutic substance delivery can create patient complications. Many drug pumps are configured, so the pump can be replenished with drug through a refill port or septum while the pump is implanted, so the period the pump can be implanted may not be limited by drug capacity. In electrically powered implantable drug pumps, the period the pump can be implanted is often limited by factors such as battery consumption, corrosive damage, and mechanical wear. The relative large size of some implantable drug pumps can limit locations where the device can be implanted in a patient. An example of an implantable drug pump is shown in Medtronic, Inc. “SynchroMed® Infusion System” Product Brochure (1995). Implantable drug pumps can use a variety of pumping mechanism such as a piston pump, rotary vane pump, osmotic pump, Micro Electro Mechanical Systems (MEMS) pump, diaphragm pump, peristaltic pump, and solenoid piston pump to infuse a drug into a patient.
Peristaltic pumps typically operate by a battery powered electric motor that drives peristaltic rollers over a flexible tube having one end coupled to a therapeutic substance reservoir and the other end coupled to an infusion outlet to pump the therapeutic substance from the therapeutic substance reservoir through the infusion outlet. An implantable peristaltic pump typically consumes energy at about 6 Joules per milliliter (J/ml) of fluid pumped. Peristaltic pumps are typically about 3% efficient in terms of electrical energy input and fluid work output. In an implantable therapeutic substance delivery device having a peristaltic pump, the peristaltic pump is typically one of the largest components in the device and can consume 90% or more of the available battery power. The flexible tube used in a peristaltic pump is typically permeable to some therapeutic substance components such as water that can then infiltrate into the hermetically sealed housing and cause corrosion. Additionally, the flexible tube can expand resulting in decreased accuracy.
Solenoid piston pumps such as variable reluctance solenoid pumps and permanent magnet solenoid pumps can have disadvantages compared to peristaltic pumps such as higher energy consumption, difficulty with passing air, difficulty with valve sealing, and therapeutic substance material compatibility. Energy consumption of a reluctance solenoid pump can be relatively high because of pump construction and nonlinear piston force. Reluctance solenoid pumps can be constructed with a large pole piece that can cause fluid energy loss. Reluctance solenoid pump nonlinear piston force caused when piston force increases as the poles close the gap can also reduce pumping efficiency. Passing air can be difficult for solenoid pumps because of large dead volumes created by valve geometries. Sealing valves can be difficult because passively operated valves can unintentionally open under some circumstances creating safety concerns. Therapeutic substance material compatibility can be difficult to achieve in some solenoid pumps because of the pumping components that are in contact with the therapeutic substance. Examples of previous solenoid pumps are shown in U.S. Pat. No. 4,883,467 “Reciprocating Pump For An Implantable Medication Dosage Device” by Franetzki et al. (Nov. 28, 1989) and U.S. Pat. No. 4,569,641 “Low Power Electromagnetic Pump” by Falk et al. (Feb. 11, 1986). An example of a permanent magnet pump configured for pumping liquids such as water or kerosene is shown in U.S. Pat. No. 5,472,323 “Moveable Magnet Type Pump” by Hirabayashi et al. (Dec. 5, 1995).
For the foregoing reasons, there is a need for a permanent magnet pump for an implantable therapeutic substance delivery device that is energy efficient, small, compatible with therapeutic substances, and has many other improvements.